First and last names are not good primary keys. There's a lot of folks running around out there who share both of 'em, eh? Adding in the middle name is an okay attempt at making a primary key, but it is also a bit risky, especially when you're dealing with a student population that has a large Indian population (in which case middle names - and for that matter, familial names - are not a given).

So since you have two different 9-digit numbers that are guaranteed to be unique - viz. SSN and student ID - why not check those before calling to tell a student that they haven't paid the loan they don't have, and so their registration may or may not be "on hold"?